Products made from or incorporating plastic are a part of almost any work place or home environment. Generally, the plastics that are used to create these products are formed from virgin plastic materials. That is, the plastics are produced from petroleum and are not made from existing plastic materials. Once the products have outlived their useful lives, they are generally sent to waste disposal or a recycling plant.
Recycling plastic has a variety of benefits over creating virgin plastic from petroleum. Generally, less energy is required to manufacture an article from recycled plastic materials derived from post-consumer and post-industrial waste materials and plastic scrap (collectively referred to in this specification as “waste plastic material”), than from the comparable virgin plastic. Recycling plastic materials obviates the need for disposing of the plastic materials or product. Further, less of the earth's limited resources, such as petroleum and polymers, are used to form virgin plastic materials.
When plastic materials are sent to be recycled, the feed streams rich in plastics may be separated into multiple product and byproduct streams. Generally, the recycling processes can be applied to a variety of plastics-rich streams derived from post-industrial and post-consumer sources. These streams may include, for example, plastics from office automation equipment (printers, computers, copiers, etc.), white goods (refrigerators, washing machines, etc.), consumer electronics (televisions, video cassette recorders, stereos, etc.), automotive shredder residue (the mixed materials remaining after most of the metals have been sorted from shredded automobiles and other metal-rich products “shredded” by metal recyclers), packaging waste, household waste, building waste and industrial molding and extrusion scrap.
Different types of plastic parts are often processed into shredded plastic-rich streams. The variety of parts can vary from a single type of part from a single manufacturer up to multiple families of part types. Many variations exist, depending on at least the nature of the shredding operation. Plastics from more than one source of durable goods may be included in the mix of materials fed to a plastics recycling plant. This means that a very broad range of plastics may be included in the feed mixture. Some of the prevalent polymer types in the waste plastic materials derived from the recycling of end-of-life durable goods are acrylonitrile-butadiene-styrene (ABS), high impact polystyrene (HIPS), polypropylene (PP), polyethylene (PE) and polycarbonate (PC), but other polymers may also be present.
Mixtures of recycled plastic materials can sometimes contain residual organic materials such as petroleum derived liquids (e.g. gasoline or diesel fuel, various lubricating oils, brake fluids, windshield washing fluids and other fluid residues) and polychlorinated biphenyls (PCBs). Such contaminants can occur on the surface and interior of the plastic pieces. These organic materials can result in problems with the end products, such as odors, difficulties with melt processing and environmental concerns.
End users require products meeting their requirements for odor, volatiles emissions and limits for PCBs, but market and legislative forces are encouraging manufacturers to incorporate post-consumer plastics into their products.
In order to satisfy these requirements, it is important to identify and implement appropriate methods to reduce the content of residual organic materials in plastics recovered from mixtures of post-consumer durable goods.
In the following, methods are described for the selective reduction of the content of organic contaminants in mixtures of plastic flakes.